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For pilots, are the procedures different between airframes with different engine options?
Lets use the B757 as an example. Engine options are PW2000 and the RB211. As I'm sure they are both FADEC engines we don't have to worry about and mechanical linkages and such. But each engine although comparable in thrust ranges have different requirements from the aircraft.
As a B757 pilot are the procedures different between the airframes with different engine options?

Are you asking only about FADEC controlled engines on large aircraft?  For example, the B206 helicopter has 2 different starting systems, the CECO and the Bendix.  Getting a CECO engine start wrong can cook the engine before you do anything about it.  Bendix starts are a lot more forgiving.

No, I'm asking if airframes with different engine options have different procedures for handling. FADEC or not. The example I used happens to have engines with FADEC.

As a general rule, you may want to wait a while before accepting an answer. Questions with accepted answers often don't get additional answers, and that may limit the amount of information you receive. I'm not implying in any way that Stefan's answer is wrong, just that someone with additional information may skip over this question because they see it has an accepted answer already.

I can only speak for the Boeing B787, but the 787 Flight Crew Operating Manual (FCOM) indicates that there are slight differences between different engine options. Three examples:

autostart modes (different failures can be automatically detected and corrected for during engine autostart),
warm-up times before take-off and cool-down times after landing,
take-off thrust setting ("GE engines: Advance the thrust levers to approximately 40% N1" vs "RR engines: Advance the thrust levers to approximately 20 TPR" - this also indicates that the primary engine indications are slightly different: N1 and EGT vs. TPR, N1 and EGT).

I don't know though how much these slight differences translate to different procedures, as I am not a pilot.

Thank you. I imagine that technology has helped as many of the functions a pilots used to have to accomplish have become automatic. My question originally stemmed from the thought that with older airframe engine combinations would this even be possible. By older I mean engines that would have had mechanical linkages between the throttle and engine. Since most engines are designed with the accessories in different locations I don't think they would be able to be interchangeable. But as I think back, offering different engine options is a relatively new idea probably dating back to the 80s.

This seems to be common difference—RR, and IAE, engines show EPR and use it as primary reference while most others have just N1. It is so on Airbus aircraft too.

@LuftBier, when there are multiple engine options, a different nacelle is designed for each. So the interface is in the pylon and the accessory layout does not really matter. Also note that while early jets were not offered with alternate engine options from the start, they were often re-engined later. Especially the military ones (air force still uses many 707-based planes, but all have modern engines).


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If DME is required, why have non-DME minima?
I was looking at the ILS or LOC RWY 9 at KJZI today and I noticed that it had lower minima for when you can identify an intermediate fix (YOCUB).  That made sense, but the entire approach requires DME.  So, if that's the case, why even bother having non-DME minima?
Both of the missed approaches require DME.  Under what circumstance could you shoot this approach but your MDA would be 520?
Here's the current plate: http://155.178.201.160/d-tpp/1609/05354IL9.PDF

Conceivably the I-ETI DME transponder could be out of service, preventing you from identifying YOCUB (unless you have a second VOR or GPS), but you could still identify BASSO on the CHS DME for the missed.

That makes good sense.  And with a single VOR receiver, you could switch back and forth to identify your IAF and JEBOP but by the time you get to 520 feet, they don't want you fiddling with your nav/com while you descend another 140 feet.  I buy that.  I'm gonna accept this answer.  I think I have a connection to someone who used to design TERPS and I'll verify that this is correct (however, I presume it is).

@ymb1, that's what I mean.  You can identify your IAF with a single VOR but once you start the approach, they want you to use the time table and descend to the higher MDA rather than switching back and forth between the localizer and the VOR.  If you have dual VOR receivers, you can identify the intermediate fixes and can descend to the lower MDA instead.

OK, I think that you can't fly a DME REQUIRED approach if your DME is out, but I can't find a regulation to reference.  This approach, as it turns out, is mislabeled and on Monday they're going to work on issuing an FDC NOTAM to correct it.
I did find a reference in the AIM that said that the DME REQUIRED in the pictograph only covered IAF through FAF, not the missed approach and that it was up to the pilot to determine if the aircraft is appropriately equipped to fly the missed.

The minima are not necessarily DME related; however you can identify the YOCUB fix using a DME.  All fixes in the approach can be identified using the localizer and the Charleston Vortac, save the BASSO hold fix, which would require a DME.  An alternate method is to use an IFR approved GPS as a 'cheater DME' (my personal term; don't try to look it up) to fly the approach if your aircraft has equipment type G and no second nav radio.

This still doesn't seem to answer the question. It specifies DME or dual VOR to use the YOCUB minima, but the whole approach is labeled DME required. If you don't have DME you can't use this approach at all, can you?

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Is a hold in lieu of a procedure turn specifically one hold on an RNAV approach?
I was looking at RNAV (GPS) RWY 6. I considered that conceivably ATC could have me enter the hold at an altitude requiring a rapid descent to get to the initial approach altitude.
I know that unless NoPT is specified on the initial segment or from the TAA sector that you must do at least 1 hold, but what I wasn't sure was could you do more than one hold at your own discretion?
So, say, you were told to cross the IAF at 4000 and you felt like losing 2000 feet in half a hold would make your passengers uncomfortable, could you just make two laps?  Would you have to ask ATC for permission first?
It looks like crossing the hold fix is your initial approach fix and then it's subsequently an intermediate fix so it seems like the design is that you enter the hold and then cross the holding fix on your way into the approach, so it seems like it's designated that you cross the fix only twice, but I wanted to be sure.
Edit:
Certainly there are exceptions.  When directed by ATC to fly a straight in approach, the hold-in-lieu is not required.  If NoPT is designated for your TAA region or on your initial segment, then it is forbidden.
To rephrase my question, given that your hold-in-lieu is required then your lower bound is 1 hold.  Is there a designated upper bound of 1 hold as well?
I.e., if a hold -in-lieu-of-procedure turn is required, is it 1 and only 1 hold?
Sorry for the confusion.

Technically it is not a holding; it is a racetrack.

@ymb1, it's not a duplicate.  I specifically mentioned that it's required at least once unless otherwise specified.  My question is specifically regarding the upper bound on the number of laps around the hold.  Is it indeed designated as 1 or is that up to the discretion of the pilot?

@J.Hougaard, do you mean that racetrack is vernacular for "hold-in-lieu-of-procedure-turn?"

@ymb1, roger.  Just didn't want it to get de-duped before I got an answer. :)  I'm pretty sure it's once, but I can't find a reg that states it as clearly as I'd like.  To be sure, I understand that all bets are off when you're getting vectored (or otherwise directed) by ATC and that, as PIC, you're welcome to make any request you feel is in the best interest of the safety of the flight.

When flying a hold-in-leiu-of-procedure-turn and the exemptions from that procedure are not met, you must fly that procedure exactly once. From the AIM, 5-4-9(a)(5):

The  holding  pattern  distance  or  time
  specified in the profile view must be observed. For a
  hold−in−lieu−of−PT,  the  holding  pattern  direction
  must  be  flown  as  depicted  and  the  specified  leg
  length/timing  must  not  be  exceeded.  Maximum
  holding  airspeed  limitations  as  set  forth  for  all
  holding
  patterns apply.
  The holding pattern maneuver is completed when the aircraft is established on the inbound course after executing the appropriate entry. If cleared for the approach prior to returning to the holding  fix,  and  the  aircraft  is  at  the  prescribed altitude, additional circuits of the holding pattern are
  not necessary nor expected by ATC. If pilots elect to make additional circuits to lose excessive altitude or to  become  better  established  on  course,  it  is  their responsibility to so advise ATC upon receipt of their
  approach clearance.

Further notes: I'm not sure quite what you mean by losing 2000 feet in "half a hold", but if you got a clearance to maintain 4000 until established, you could start your descent immediately after crossing ODAZO, giving you 8 miles plus a one-minute turn to descend. At 120 kt, that's 4 minutes for the 8 miles, so 5 minutes for 2,000 feet or 400 ft/min - perfectly reasonable.
Finally, you mention that "When directed by ATC to fly a straight in approach, the hold-in-lieu is not required." Your statement should be stronger: as when NoPT is printed on the chart, a straight-in clearance forbids the procedure turn/HILOPT unless you ask for and receive approval from ATC.

Awesome answer!!  Thanks @NathanG!

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What happens to EGT after a bird strike?
I just watched the movie "Sully", and I really enjoyed the effort put into making the movie as accurate as possible.  As I'm working towards my PPL, I decided to apply some of my new aviation knowledge when watching the movie.  I especially focused on the center MFD.  I understood everything I saw, except for the Exhaust Gas Temperature (EGT) readings after the bird strike.  I noticed that Engine Pressure Ratio (EPR) and N2 fell, but EGT stayed in what looked like roughly the same position.  I would have expected EGT to fall after the bird strike destroyed the engines, but it didn't.  Is this normal?  Did the flames seen coming out of the engines cover up a fall in EGT?

Normally, I wouldn't, but these looked really close to what I would have expected to see.  Even if this is a mistake, the rest of the cockpit displays looked pretty good to me, which is pretty cool since a lot of movies tend to ignore those kinds of details.


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Should I monitor the emergency frequency (121.5 Mhz) at all times?
When flying on a plane with two or more radios, should I set the second radio to 121.5 at all times? (Assume I'm not using it to listen on other frequencies)
I've heard that sometimes when an intruder penetrates restricted airspace, the military will broadcast on this frequency in an attempt to communicate with that aircraft. Is this a good way to avoid me getting shot?
What about monitoring in case someone around me has an emergency?
Is there a difference in general aviation vs commercial airlines?

EDIT: I'm asking about whether this is a good idea, not about regulations.

Are you asking about a specific country, or is it a general question?

There is no requirement for this, if that is what you are asking? Are you asking about regulations? FAA recommendations?

@Pondlife I'm asking about recommended procedures, as in is it a good idea.

Are you expecting to penetrate restricted military airspace??? O_o

Nah, you can wait til after the F-16 goes knock-knock, at that point, you picking up the radio and talking is the best possible outcome for them.

Do each of your radios have the ability to set an active and a stand-by frequency (to easily switch between them), or can each radio be used to select only exactly one frequency at a time? How about dual-watch capability?

Airlines routinely set comm 2 to 121.5 when they don't need it for talking to company or getting ATIS.  But for a light aircraft pilot in busy airspace, the second comm is a really useful tool for reducing workload by being able to preset frequencies, and dedicating the second comm to 121.5 all the time takes that feature away, for the very small chance that you're hear someone's ELT go off or broadcast an emergency that will be heard by ATC anyway.  Very few GA pilots monitor guard frequency regularly.
On the other hand, if you are flying over a remote area, it's not a bad idea at all and you could save someone that crashed with a non-406 ELT.

There's also a new low-level frequency now in the UK

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How much does the landing gear compress on a fully loaded airliner on the ground?
When an empty airliner is loaded with passengers, cargo and fuel, the extra weight compresses the gear strut and it sinks. Jet bridges are designed with this in mind.
How much height does it actually sink?
For the purpose of the question, I am interested in any typical commercial airliner models.

The value will obviously vary for different aircraft models (and also with the loading, c.g. location etc), but the usual range can be found in the airport planning document for the particular airliner, where the values for ground clearance for the aircraft at the OEW (max. value) and MTW (min. value) would be given. The difference should give you the compression.
For example, for Boeing 737-800, the quoted value is around 15 cm (plus or minus 7cm).

Image from 737 Airplane characteristics for Airport Planning document
Note that the different parts of the aircraft 'sink' different amounts- the fuselage sinks around 15cm, while the engines (mounted on the wings) sink more- by 16cm due to the fuel in the wings.
Another 'typical' aircraft, the A320neo sinks by about 10cm.

Image from A320 Aircraft characteristics for Airport Planning document
Note that the values are given here for max. ramp weight.

the engines (mounted on the wings) sink more- by 0.16m due to the fuel in the wings. not only because of the fuel, but mainly because of the cantilever, concentrated load, and deceleration. an empty wing would still "flap" and sink more than the fuselage.

For example, for Boeing 737-800, the quoted value is around 15 cm (plus or minus 7cm). That's a heck of a margin!

The answer provided by @aeroalias is good.  I'd add that in addition to loading, it also depends on the nitrogen pressure in the gear struts as well as ambient temperature. My background was military; there we might adjust strut pressures based on mission loadings (fuel, ammo, external stores).  While I wouldn't expect airlines to adjust pressures between flights, I would expect them to set them based on typical fuel load and temps for the routes a given airframe is projected to fly.
While the goal of all of this nitrogen pressure adjustment is to maintain a range of strut extension heights considered safe by the manufacturer, the fact is that, when the aircraft is loaded near the upper or lower bounds of the range the nitrogen pressure is set for, or when an aircraft transitions between temperature extremes, you can still get some interesting strut conditions, either low or high.
I'm going to qualify everything I just said with the caveat that newer aircraft might be shipping with autoleveling systems -- someone else might know more about that.

Quite a few military aircraft can actively control the nitrogen pressure to shorten the landing gear leg for retraction (the Saab 35 Draken would be one fine example), so they can even adjust the pressure during a mission.

I was wondering if there was a mechanism to adjust the pressure dynamically. Do you know if this feature is on any civil commercial aircraft?


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How much force is needed to tow an airliner?
Airliners are often (almost always actually) pushed back by a tug or a tractor to leave the gate. The tug can also tow an aircraft that cannot taxi by itself.
How much force is required to pull or push a large airliner on the ground? In other words, what is the horsepower of these tugs?
EDIT: By large airliner, I mean Boeing 747 / 777 / A380 type, the ones which ATC append "Heavy" (or "Super") to their call sign.

There are many types of tug for many types of aircraft.  Are you able to be specific, otherwise the question is a "list".

Every year at the airshow my company brings an A300 and they tie a rope to the front gear and 15 of us pull it, tug-of-war style.

Depends on the surface, and whether the tires are inflated properly.

You asked for force and horsepower, which are different thing. Force should just be $F=\mu N$. HP will be based on how quickly you want to accelerate. Right?

Moving planes is pretty easy. They are lighter than they look. A single person can drag a twin engine.

A part of a Toyota ad, they used a Tundra to pull the Space shuttle Endeavour.  While not a "heavy" aircraft, the forces are similar:  https://www.youtube.com/watch?v=AO37TSgKwSg

@TylerDurden: Twin-engine as in a Cessna 310, or twin-engine as in a 777?

Tugs do not need that much horsepower, even the biggest tugs only have around 400bhp. What they do need is lots of torque for push/pull power, lots of weight to give it plenty of inertia, and big grippy tires to transfer the power to the surface.
The T80 in this link is pretty typical, 50-70 tons, 408bhp, and 1500 pound feet of torque. That's more than triple the torque of a hefty pickup.

As Carroll Shelby once said, "Horsepower determines how fast you hit the wall, torque determines how far you move it." Think of the plane as a wall that the tug doesn't need to move quickly.

Why does a tug need inertia? Surely the weight is actually to give as much traction as possible to avoid the tug's wheels slipping when the power id applied.

It's weight helps to give an even pull, if a tire loses grip it's momentum will help keep the assembly rolling in the same direction.

Seemed like a reasonable edit, @GdD, especially the "Drawbar Pull" bit. But, it's your answer.

Thought for a minute you meant the T80 tank!  The tug is actually heavier, is it full of concrete?

It only takes 7030 Kg, 309 BHP, and 553 lb/ft of torque. Well, it does if your tug is a VW Toureg.
Very pixeley image sourced from link above
This was a stunt done by the TV Show Fifth Gear and Autocar magazine. Realistically it doesn't take much, but I wouldn't count on the Toureg for day-to-day movements at JFK, ORD or ATL.
No, that's not a standard 747-200, it was modified for the James Bond movie Casino Royale.

My brother still will not believe that they used a modified 747 for that movie. I noticed it immediately when it came out.

As a random aside, that craft is featured rather heavily in the new/old Top Gear.  They actually did a "drag race" with it once, were Jeremy was tugging it along in a Tractor.  He got last place, it's a huge thing to be pulling...

@JayCarr, really? Jezza actually lost some sort of Top Gear Challenge? I'm going to have to go re-watch them all to find that one!!

I don't know where you got your stats from but, according to Volkswagen a VW Tuareg has a maximum gross weight of 2910kg and puts out at most 406ft-lb of torque (and even that's cheating by taking the maximum weight of one model and the maximum torque of a different one).

Directly from the linked article, @DavidRicherby.

@FreeMan Ah. In that case, you should probably say, "If your tug is a VW Tuareg with its weight more than doubled by adding steel ballast." Interesting that that article contradicts VW's own technical specs about the torque of their car's engines.

@DavidRicherby everything I can find (in a super quick Google) for the V10 Toureg TDI shows 553lb/ft. Sure you're not looking at the V6 specs on the VW site?

Actually Boeing (publicly) publishes this data for all of its aircraft in the Airplane Characteristics for Airport Planning Manuals. Here is the chart for the 747-8:

The "Total Traction Wheel Load" is the required weight of the tug on its drive wheels, while the "Drawbar Pull" is the force on the actual towbar/NLG.

Actually, friction of the wheels, and the slope of the concrete is all you need.
 "Strongmen" pulling buses only have to pull 300 pounds, once static friction is broken.
    See explanation HERE
416,299 pound planes (188.83 tons) like the CC-177 Globemaster III cargo plane can be pulled by It is MUCH BIGGER than a jumbo jet.
Youtube is full of videos of people pulling planes with teeth or "other" body parts.
110 BHP is the rating that the "AIRCRAFT TOWING TRACTOR – MODEL BA10G40" claims. It hauls 737's at up to 25 kmph.
See full stats HERE

If by "jumbo jet" you mean 747, it's much, much (448 tonnes MTOW) bigger than a C-17 (265 tonnes).

Particularly the second paragraph looks like it needs some editing, but I don't know what was meant to go in there. Please review it and [edit] appropriately.

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text:
How do piston engines deal with sea spray (saltwater ingestion)?
From my related question, I want to know about sea spray being ingested into a piston engine during flight. Will this immediately corrode the engine unless there are special materials?
I'm asking this for piston engines, not jets or turboprops. I'm especially interested in WW2-era planes.
Obviously this is primarily about naval aircraft built for saltwater environments, but I'd like to know the protection measures so I can see if a land-based aircraft can be easily modified, or if it's going to need an entirely new engine.
Note: At very high temperatures, corrosion is much faster. I don't know the math for corrosion, but my worry is that sea spray in the engine could cause some cracks somewhere after just a few flights, unless things are made from a much higher (more expensive) grade of stainless steel or aluminum alloy.

Seaplanes operate from coastal saltwater all the time, ingesting lots of seawater, and they don't do anything special to the engines to deal with seawater ingestion.  The effort is mostly on keeping salt rinsed from the airframe and engine externally and they normally get a fresh water rinse at the end of the flying day.  Some operators may spray nicely atomized fresh water into the engine intake while running it to rinse salt from intake passages and carburetors etc, when they are doing the external bits.
The other measure is keeping the protective coatings intact, including the paint on the engine.  You really don't want salt on an engine where paint is flaking off aluminum fins or areas of the head, because corrosion pitting results that leads to cylinder head cracks.
So the main protection measure is, keep the salt rinsed off as much as possible with fresh water, and maintain the protective coatings. Even with all that, coastal aircraft operating daily from seawater year-round often require airframe rebuilds to deal with corrosion maybe every 10 years or so.
In any case there aren't any physical modifications you can do to an engine.

Well at very high temperatures, corrosion is much faster. I worried that it could cause some cracks somewhere after just a few flights, unless things are made from a much higher (more expensive) grade of stainless steel or aluminum alloy. I shoulda put a note of that in the OP, will do so now.

On the other hand, a wooden boat sailing in salt water should be rinsed only with salt water, never fresh.  Removing the salt would let mold grow.  Maintainers of early seaplanes would have learned that from their fellow mariners, at least for the wooden floats if not the fabric skins (and engines!).

Corrosion is not something that occurs "immediately". It happens gradually, when a metal is exposed over a long period to an environment that degrades it (such as a salt water environment, indeed).
The parts of an aircraft that are most at risk from its environment are the parts that are exposed to it, and not the internals of its engine.
Inside the cylinders, and other parts of the engine such as a carburettor, the conditions are extreme (high pressure, near vacuum, high and low temperatures, presence of concentrated substances, etc, and rapidly-changing).
A little bit of salty moisture that manages to get in is going to be swept away from those internals pretty swiftly. In the cylinder, the cylinder walls and the piston are also wiped (several times a second) by their own movement.
Inside the engine itself is not really an environment in which corrosion can get started.
That said, salt water generally isn't very good for machinery, and there will probably be other internal parts where salt and moisture could hang around longer and cause a problem, especially where there are two different metals in contact with each other.
The remedy in these cases is not special materials, but maintenance procedures.

I meant more like after a few flights. At high temperatures, like in an engine, corrosion is much faster. I put a note of it in the OP.

Corrosion internally is not so much from moisture or salt.  The parts are all coated in oil.  It's corrosive compounds that build up in the oil itself.   Seawater operations might result in trace amounts of sodium in cylinder blow by but it's the acids formed from other combustion products that are the problem.  Lycoming cams are particularly susceptible to this, but it requires the engine to sit for very long periods before significant corrosion gets established.  For an airplane flying regularly, internal corrosion is simply not an issue, salt water or not.


text:
Does an uncovered naval aircraft suffer any weathering affects?
This question is for WW2-era naval aircraft.
I noticed that some cruisers and battleships carried a couple seaplanes, launched by catapult and recovered with cranes.

Obviously these are unprotected by a hangar. So it raises the question, is a hangar really necessary to protect naval aircraft from the weather? Naval aircraft should be more stalwart against seawater at the very least, and I can't imagine that freshwater rain would do anything to even a land-based plane. Dirt and sand also seem a remote possibility. Only thing left I can think of is sunlight over long periods.
The question pertains to seaplanes as well as wheeled aircraft, if they are carrier aircraft. (I understand that carriers have a hangar for maintenance and/or an armored roof, but my question is about the need, or not, for weather protection.) Can naval aircraft just be left on the deck without ill-effects?

That's a Curtiss SOC Seagull. It had an operational life (first flight to retirement) of 11 years. If the F-35 was treated that badly, they would have all been retired by 2017.

@Coomie 11 years sure, but that alone does not prove it was due to harsh weather or bad maintenance. This was WW2 when technology was rapidly progressing. Any bi-plane was already obsolete by the time WW2 started anyway.

Aren't the main reasons carriers have hangers a) so that planes don't take out half the ship's air arm if they botch a landing and b) to protect the planes from air attack, with weather being at most a minor consideration?

Naval aircraft cannot be just left on deck without maintenance and expected to operate after an extended period of time. I will restrict this to storage on deck and avoid going into operational issues like spray effects on engines as OPs question does not ask that.
There are a multitude of technologies in use to protect metal parts from corrosion, but in the end these all fight a losing battle against entropy and their effectiveness is more accurately measured in how long they can stave off corrosion.
Painted parts are probably the most resistant, as organic coatings provide a hard barrier over the vulnerable surfaces. Paint is not foolproof, however, as it can chip and crack, due to thermal stresses, FOD, etc. Furthermore, not all parts can be painted and corrosion can develop underneath paint if it has an entry point, like a rivet hole , a static discharge connector or a crack in the paint.

Where organic coatings are not suitable, for example on shock absorber struts, other coatings can be applied. For steel a common solution is a chrome layer; for aluminium, chromate conversion and anodizing. These solutions are not as effective as a coat of paint, and an aggressive-enough environment will attack even chrome layers. As an example, take landing gear struts, which have multiple exposed moving parts, many crevices to accumulate moisture and diverse metals ready to form galvanic cells.
Finally, there are places where no coating can be used at all: static dischargers. These do exactly what the name implies, ground the aircraft to allow for built up static charges to flow into the ground, so they need to be exposed and to contact (almost)bare metal on the airframe to ensure conductivity. Their connection points are typically covered in sealant after installation, but these sealants do not last forever: they weather and end up cracking after some years in the field, turning into a moisture trap and destroying the part they are on if not monitored.

Finally, a note on composite airframes.
CFRP parts are conductive and very noble, so they can easily corrode whatever metal is attached to them. This can be mitigated with careful engineering, but can come as an unexpected problem for systems suppliers that are used to installing equipment on metal airframes: an aluminium airframe will corrode before a steel tray attached to it without insulation, but the opposite will happen with a composite airframe.

Can you comment any on the photo then? Were those exposed seaplanes not expected to last longer than a year? 2 years? Or maybe they were supposed to be covered by a tarp? Also, i did not explicitly mention spray effects, but i think that qualifies as weather for a naval aircraft. Maybe you can expound upon that, but if it is too big a topic i will open another q on it.

Naval aircraft on an aircraft carrier are either parked on the flight deck or the hangar bay.  Hangar bays have huge side doors that close, but typically they are only closed in foul weather and normally left open.  Aircraft in both places are quite exposed to breezes of salty air, which are quite common when the ship is traveling at 20-30 knots.  Covering aircraft with tarps is not practical because the aircraft need to be accessed, maintained, and used frequently.

Sorry, I was speaking of modern aircraft carriers.  It may have been practical for the seaplanes carried by WWII-era cruisers and battleships to be covered by tarps.

in WW2 planes were initially often carried inside a hangar, fueled and ready to go. After the first few naval battles led to ships being lost due to hangar fires set off by a single shell hitting the hangar and turning those planes into torches, fueled planes were kept outside and/or the hangar doors open in order to make it easier to throw the planes overboard when and if a fight started. And yes, that does decrease the service life of the plane, but planes are a lot cheaper than heavy cruisers and easier to replace as well.

@DrZ214 I do not have enough knowledge of the operational procedures for interbellum observation planes to comment directly, but a quick search does point to an early retirement for the entire fleet. I'll try to find more, but information about the storage procedures for embarked aviation from 75 years ago is hard to come by. On the issue of spray, for stored airframes it only helps add saltwater to inconvenient places; for operating aircraft it is more troublesome as it can be ingested by the engines, but all naval craft have some design requirement to withstand this.

Your last point seems like me to be a pro, not a con.  Better to have some piece of ancillary equipment corrode than to have the airframe itself corrode...

@Sean Not quite; modern naval aircraft are complex systems where the airframe is not necessarily the most important part. All the ancillary systems are its raison d'etre, and some are outright critical: the landing gear, for example, tends to be made of steel.

@AEhere: You can still fly, and even land, with broken landing gear.  Flying, and landing (in a controlled manner), get to be somewhat difficult if your aircraft falls apart in midair.


text:
In a turbofan, why are there no stators behind the fan?
Why are there no stators behind the fan? At least, I've never seen any turbofan design that has stators right behind it. (Here is the latest turbofan I've looked at, the CFM56. Cutaway part starts around 00:35.)
The purpose of stators is to redirect the airflow to be mostly axial. Without them, the air would be spiralling too much.
The fan is the biggest compressor so I would think stators are needed there more than any other place, but apparently that's wrong. I just do not know why it's wrong.
Edit: Yep, there are stators there after all. Just because they're not shown in a video doesn't mean they aren't there. Oh well.

I'm not sure your premise is correct. AFAIK, turbofans do have stators in the bypass flow. If you go through the cutaway video you link to frame-by-frame, you can see them.

This video is a bit misleading (higher resolution video). At 0:54, by some difficult to understand camera displacement, the booster stators start contra-rotate and the rotors become stationary except the fan. At least, the booster rotors and the fan should be synchronous (N1).


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Do fighter jets have an auxiliary power unit?
Do fighter jets have an auxiliary power unit? If they don't, then how does the propulsion/ignition process start in the engine?

Some do some don't. For some planes it is an unnecessary weight for flight so the aircraft are started with a starter cart pulled by a ground vehicle.
http://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/197634/ma-1a-start-cart/

Most current fighters do.
A notable exception is the F-16. The F-16 has a "jet fuel starter" (JFS), which is a small jet turbine started by a bottle of compressed air. Unlike a normal APU, the JFS is linked directly to the main engine, so the only thing you can use it for is to start the main engine.
An APU can also provide backup electrical power. Since the F-16 doesn't have one (and is a fly-by-wire aircraft, which requires electrical power for normal operation), it has an emergency power unit (EPU) instead. The EPU uses a special fuel called H-70, which is 70% hydrazine, and 30% water. Hydrazine (normally used as rocket propellant) doesn't require an external source of oxygen. It carries its own oxygen supply; expose it to iridium and it immediately (well, within a couple milliseconds, anyway) starts to release large quantities of hot gas. This runs a small turbine, which can restore power within about 2 seconds. The main shortcoming is that hydrazine is quite hazardous (though the 30% water content of H-70 renders it substantially less hazardous than pure, anhydrous hydrazine).

Hydrazine doesn't exactly burn when it decomposes (because it isn't a redox reaction between an oxidiser and fuel), but it does get very hot in the process, so it's near enough. It essentially just falls apart from a liquid into [mainly] two gasses, massively increasing the volume (as in an explosion) and getting very hot. But that's just semantics, really.

To address the "how" part of the question - non APU equipped jets use some method to start the engine spinning to initiate airflow through the engine.  The JFS in the Viper powers the main gearbox, which is connected to (and spins) the compressor core.  Same idea, different execution with jets that use a huffer cart.  A prime example is the T-38 with the J-85 engines.  The air cart spins drives compressed air through the core, spinning up the engine.  The igniters will initially be fired by the battery or by a generator.

Yes, internal starting systems are found on most modern fighters, however be careful how you define 'modern'.  In my usage, 'modern' means anything designed and built in the 21st century, but many nations are using aircraft built decades ago, so a particular fighter may be very common and effective yet not technically 'modern' e.g. the F--15 and F-16 come to mind.  The F-16 starts the engine using the Jet Fuel Starter which receives its initial pressure to spin from the JFS/Brake Accumulator bottle which is a dual-purpose system as the name denotes.  It dumps pressure into the jet fuel starter which in turn is used to start the engine.  If the accumulator loses its charge, the crew chief and/or a friend or two connect a 3-foot t-handle underneath the left main landing gear well and pump the accumulator back up to pressure to allow an engine start to be performed.  A detailed example of the start procedure is here:  https://www.quora.com/How-do-you-start-the-engine-on-an-F-16-Fighting-Falcon .  Certain fighters without an internal starting system can be started via an air-start system (like the T-38/F-5) connected externally by the ground crew or a cartridge start which is a chemical charge (think of a shotgun shell) to get the engine rotating, a whopping-great example of which follows here for a German F-4

THE USAF also used the starter cartridges on larger aircraft like B-52s and KC-135s. Seeing 6 B-52 fire 8 starter cartridges each make an impressive cloud of smoke. They would shut down 2 of the engines so the cartridges could be removed, the area cleaned, and new cartridges installed. Then shut down the other 6 engines and do the same for them,

It all depends on the airframe you’re talking about. Early fighter jets use pneumatic starters with air supplied by external start cart.  Larger, powerful, and modern jet fighters  are usually equipped with some sort of gas turbine auxiliary power unit used for engine start in the event that external power sources, whether electric or pneumatic, are not available.


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F-16 "training rounds"?
From this Wikipedia article

A fighter pilot based at Andrews Air Force Base, Billy Hutchison, claims that while in the air he spotted Flight 93 on his scope and planned to first fire his training rounds into the engine and cockpit, and then ram the airplane with his own jet.[135][136]

One of the references refer to these as "practice rounds".
What are practice rounds? Are these a special type of ammunition with inferior performance to standard ammunition for the M61?
From the M61 article I found that these rounds appear to exist: "PGU-27 AB training rounds"
Are these the correct rounds the plane was supposedly loaded with?
The article seems to claim they are both cheaper and more effective than standard rounds, but maybe I'm reading it wrong.

Less effective.  20mm projectiles are normally explosive.  Training rounds are non explosive, basically really big bullets, and are coloured blue.


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What is the relation between missile fin deflection limit and altitude?
What's the relation between limit of deflection for aerodynamic control surfaces (tail control) and altitude for surface to air missiles?
Also how can the fin deflection range (Max/Min) be determined for any altitude?
Please mention any reference text related to the subject.

From Missile Guidance and Control Systems by George M. Siouris, I know that  Maximum fin deflection is limited by the missile velocity and
the altitude band in which the missile is flying but i cant find any procedure to determine this upper limit.


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What is the range of frequencies of vibration in a helicopter due to the main rotor alone?
Vibration in helicopter can be caused by many different reasons. I am interested to know what is the range of frequencies of vibration due to the main rotor alone?
I understand that it would depend on the helicopter type. So any reference to such analysis would be appreciated.

The vibration from the main rotor (and of the tail rotor) are harmonics of the Blade Passing Frequency: number of blades times rotational velocity. This site contains some data on the Blade Passing Frequencies of some helicopter types, for analysis purposes for military helicopters which must comply with MIL-STD-810F.
Image source

MIL-STD-810F, Method 514.5, paragraphs 2.2.6 and 2.3.3 are concerned with the vibration levels that helicopter components and cargo must withstand.
The helicopter vibration environment is a combination of many sinusoidal components due to the main rotor, tail rotor, gearbox, and engine.

Image source
Since the vibrations are also imparted on the surrounding air and then onto the fuselage, acoustic measurements are a good indication of the mechanical vibrations as well. Above graph shows acoustic measurements of seven Hueys flying by, and shows harmonics at intervals of 12 Hz. From the referenced article:

The first notable peak occurs at 24.0 Hz. A series of harmonics occur at 12 Hz intervals thereafter. These are the blade passing frequencies of the main rotor.
The main rotor blade passing frequency is: 5.40 Hz x 2 blades = 10.8 Hz
The Doppler shift increases the apparent blade passing frequency to 12 Hz. The theoretical speed of the helicopters was 76 mph based on this shift.

An interesting factoid is that the highest peak is not caused by the main rotor but by the tail rotor: the one at 123 Hz.
The highest main rotor vibration peak occurs at 60 Hz, five times the main rotor Blade Passing Frequency. There are still noticeable 12 Hz peaks at up to 300 Hz sound frequency = 270 Hz frame vibration frequency.

EDIT

This presentation shows vibration measurements taken off of an unnamed helicopter. The rotor frequency is detectable as a small peak, the blade frequencies are much more dominant.

The links discuss acoustic frequency, will the spectrum be different if we place a sensor at the body of the helicopter to measure movement/vibration of the structure?

@Creator The acoustic vibrations have the same source as the mechanical vibrations. There will be a difference in the amplitude of the different frequency ranges when measured directly at the frame, as acoustic propagation has different damping characteristics than mechanical propagation. But the general trend will be similar: harmonics of the BPS of main rotor, tail rotor, transmission gear wheels, turbine & compressor BPS.

Does the acoustic spectral peaks depends on the number of blades? I assumed it does. Is the structure vibration would be dependent on rpm alone? I understand your point that the source is same only the medium of the wave is different (air and surface). Would you help to clear my confusion?

Good question. The structural vibration would also be a function of number of blades: if you follow a blade throughout a revolution it tilts up and down, lunges forward and back. The acoustic vibration mainly picks up the blade lift pulse as it passes a ground observer, these are also imparted on the fuselage, through the air in between the rotor and fuselage. Mechanical vibration would look different for different hub layout, a teetering rotor like the Huey has does not allow for individual blade lead/lag motion.  But still the blade passing frequency would be visible on mechanical vibration.

Thank you. I am interested to know the lowest spectral peak (like resonance not harmonics) at the structure of an helicopter for rotation of the main rotor. Can I assume it is approximately proportional to the product of number of blades in the helicopter and RPM of the main rotor?

Yes the rotor rpm does show up in a spectrum but the peak is not very high. There is a vibrational spectrum in this presentation, I'll add to the answer later in the day.


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How to adjoin wing skin to wing ribs?
I saw a youtube video (from a channel called Real life guys) where gum was used to join the ribs of their homemade plane to the skin and I saw another video where the wing skin(tedlar) was literally sown to the ribs of the wings,my question is what is the appropraite way to join the  wing skin(tedlar/mylar)to the ribs?

I did a search for tedlar, and then tedlar/mylar, and came up with this at Dupont.  Is this the materia being used?  http://www.dupont.com/search.html?ss=&site=default_collection&output=xml_no_dtd&q=tedlar%2Fmylar&SiteSearch_SiteSearch2Button=

Tedlar by itself seems to be a film, while tedlar/mylar would seem to be sturdier stuff, Tyvek  being nailed to houses under the siding as a windblock I think.  Glue for the first and sewing (similar to the stitching done on tube & fabric planes) could be appropriate for the second.

Rib stitching is actually a standard practice and has been since at least the 1940s, probably much earlier.

@acpilot: Rib stitching is as old as using fabric covering. The peel stress on the upper surface will make every glue fail - you need to stitch to make the fabric stay on the rib!

The correct way to use is the way mentioned in the construction manual for your kit plane.

The FAA offers a nice handbook on wing skin covering for fabric aircraft you can find here. They list, clips, screws, rivets and lace as the joining methods

(source)

Rib Lacing Cord
Rib lacing cord is used to lace the fabric to the wing
  ribs. It must be strong and applied as directed to safely transfer
  in-flight loads from the fabric to the ribs. Rib lacing cord is
  available in a round or flat cross-section. The round cord is easier
  to use than the flat lacing, but if installed properly, the flat
  lacing results in a smoother finish over the ribs.

In some cases, or even in adition to other methods fabric cement may be used.

Fabric Cement
Modern fabric covering systems utilize special fabric
  cement to attach the fabric to the airframe. There are various types
  of cement. Figure 3-9In addition to good adhesion qualities,
  flexibility, and long life, fabric cements must be compatible

Tedlar is DuPont's brand name for a polyvinyl fluoride foil. Chemically it is between polyethylene and PTFE (brand name Teflon), and the strong chemical bond of the fluoride atom gives it good weather resistance and gas tightness. In aviation its only use is in the decorative cover of internal cabin surfaces.
Mylar is DuPont's brand name for a biaxially stretched polyester foil which has high mechanical strength but low resistance to ultraviolet light. It is used for blister packages or soda bottles. For aerospace applications it is made gas-tight and UV resistant with a metallic layer of a thickness of only a few atoms. Such metallized films are used for thermal blankets, in spacesuits, on satellites and for toy helium balloons.
Both materials are sold as foils (or films), and this makes them rather unsuitable for covering aircraft surfaces. A proper cover material should be a fabric, for three reasons:

Fabrics can be tightened after application, for example by the application of dope.
Fabrics are better for draping around spherical surfaces. Depending on the type of weave, this capacity is rather limited, but still much better than that of films which need to be plastically deformed in order to assume a three-dimensional shape.
In fabrics, stitching will not introduce local defects but leave the tensile strength of the material intact.

Bonding or glueing alone will not be sufficient to permanently attach a cover to a substructure, because in low-pressure regions the cover will be sucked away from the structure. This results in local peel stresses which are certain to destroy the bond over time. @Dave's answer gives a good overview how to avoid peeling - be sure to pick one of the methods it shows.
Model aircraft use special polyester foils which have been stretched and will contract under the application of heat. On one side they are covered with a hot-melt adhesive. Their easy application has made them supplant most other covering materials, and the web has many pages with instructions for their application. However, for man-carrying aircraft they are too thin and offer too little strength.


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How to calculate Reynolds number?
How do I calculate the Reynolds number of a wing with wing chord,1.2m and speed of 60km/h

One way is to see what the following NASA links have to say about it and possibly using the calculator they have at the bottom of either page.
https://www.grc.nasa.gov/WWW/K-12/airplane/viscosity.html

The similarity parameter for viscosity is the Reynolds number. The Reynolds number expresses the ratio of inertial forces to viscous forces. From a detailed analysis of the momentum conservation equation, the inertial forces are characterized by the product of the density $\rho$ times the velocity $V$ times the gradient of the velocity $dV/dx$. The viscous forces are characterized by the viscosity coefficient $\mu$ times the second gradient of the velocity $d^2V/dx^2$. The Reynolds number $Re$ then becomes:
$$Re = (\rho \cdot V \cdot dV/dx) / (\mu \cdot d^2V/dx^2)$$
$$Re = (\rho \cdot V \cdot L) / \mu$$
where $L$ is some characteristic length of the problem.

and

The dynamic viscosity coefficient divided by the density is called the kinematic viscosity and given the Greek symbol $\nu$
$$\nu = \mu / \rho$$
$$Re = V \cdot L / \nu$$
The units of $\nu$ are length^2/sec.

https://www.grc.nasa.gov/WWW/K-12/airplane/reynolds.html

The Reynolds number expresses the ratio of inertial (resistant to change or motion) forces to viscous (heavy and gluey) forces.

I've edited the post for you, but please consider revising my edit and adding any extra information you think should be added.


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How to locate the coordinates of the Center of Gravity of an airfoil?
I am working on the inertial effects on a variable pitch propeller and i need to define the location of the center of gravity on the airfoil to calculate moments of Inertia and angular momentum. What is the best way to do it?

The same way you locate the center of gravity of any object. If it is very simple you do summation. If it is a curve defined by a formula you do integration. If it is anything else you use numerical methods.

You can get reasonably accurate results by cutting a piece of plywood with the form of the profile, suspending it at three different points, and then mark the prolongation of the suspension cord on the profile. The intersection point of the lines (or the center of the small triangle, if one is thus generated) marks the c.g.

Perhaps a question for you would be this -- are you trying to determine the CG location analytically and experimentally?  It sounds like you're trying to design the prop on paper and do some design studies...so my second question is this: what are you trying to do?

@Marius Yes, actually i am designing a propeller blade with the pitch axis placed in an offset distance from the aerodynamic centre or CG. So i am trying to calculate the pitching moments due to mass/Inertial effects, and i need parallel axis (Steiner's) to make the calculations which are made with the CG location as a reference.

Oh ok.  I just had to do something similar for computing aeroelastic effects on a wing.  The only way I saw how to do it was to make a little calculator that would compute the cross-sectional properties for me.  Essentially, it's the same of @kevin's comment -- just integrate to find the cross-sectional properties given some desired skin thickness.
I don't know if there is a "best" way to do what you want rather than just creating "a tool that does what you want" based on the design of your cross sections.  What do your cross sections look like, and what airfoil(s) are you using?

@Marius i am working on an Eppler airfoil E326 with reflexed profile; data can be found here: http://airfoiltools.com/airfoil/details?airfoil=e326-il. So by integration you mean this formula : $$ R_{cm}=(∑_i(m_i*r_i) /∑_im_i ) $$
where R and r_i are the position vectors x,y,z right?

@george -- Exactly.  "m" can be a density to make your life a little easier too.  You can use a program like XFLR5 to add points to the E326 profile too for a little more accuracy/control if you decide to have a non-homogenous interior.  What does your interior structure look like?  I'm assuming you're adding weights, etc. (as I note, I'll codify this into an answer soon along with some geometry formulas for calculating moments of inertia, etc.)?

@Marius yes, actually i need to predict the static and dynamic balance/stability of the propeller by equating the pitching moments due to aerodynamic loads with pitching moments caused by  the inertial effects. Have you any idea on witch theoretical background shall i consider? I am assuming angular momentum would be useful but i am not sure.

@Marius Also, i am going to use a  High Strength Carbon Fiber /Epoxy Composite for the blade. Is that what you mean by interior structure?(I have already got the properties of the material)

@George Ooo...designs using composites are another can of worms that's a little beyond my expertise.  I have some reference texts that I can note, though.  By internal structure I was also referring to how you were going to balance and tailor the blade structure to achieve dynamic stability.  I have a reference text that may come in handy for that too, but estimating the strength of composite structures...that's tricky.  I'll see what I can find.
By the way -- it would be useful to update your question with some of this detail, and then rephrase your question as looking for a method.

@Marius Basically, i will not give much emphasis on the material of the blade since i am trying to develop a propeller for small RC UAVs. Also, the purpose is to find out weather it is feasible to develop this kind of "self adjusting" pitch propeller tailored only due to aerodynamic loads. That's why my idea was to pivot the blade in an offset from the a.c. Counter weights are going to be used to achieve the dynamic stability, but i have no idea what calculations needed yet.

@George Gotcha.  Alright--I think I have some resources for you.  And some papers...someone else in my graduate lab was working on the next step of this idea for a large-scale rotor.  Hopefully have it written up today or tomorrow.

@Marius Legend!

To compute the inertial properties of your blade, you need a couple of things: a way to compute inertial and elastic properties along the blade, a blade layout, and some idea of the expected load you want this to carry.
Starting with elastic properties--this can be either really straightforward or VERY tricky, especially when you start throwing composites around.  That said, this is true primarily because composites can be tailored into having just about whatever material properties you want...but the analysis of composites for essentially what you're doing was the PhD dissertations of two grad students I know.  The one is developing an analysis tool for aeroelastically tailored blades (also mentioned here, in a study by Sandia National Labs: http://energy.sandia.gov/wp-content/gallery/uploads/SAND2001-1303A.pdf), which sounds like what you're trying to do.  In short, these blades take advantage of strategically tailored material properties in order to achieve variations in blade twist purely based on a blade's operating condition.  If you are going to develop your own composites design code (or have one!), I think this is a feasible goal and I'd recommend you to "Analysis and Performance of Fiber Composites" by Agarwal, Broutman, and Chandrashekhara for an intro to composite analysis.  Based on that text, you could develop an analytic design code that might get you into the ballpark, and maybe start developing some finite element models to go beyond that.  It requires a fair amount of setup, and, since I don't think it was the main thrust of your question, I'm not going to write it out.
I think it suffices to say that back-of-the-envelope estimates for composite materials are hard to come by.  That said, it can be a rough approximation to treat composites as "black aluminum", or as an isotropic material with the bulk mechanical properties of the material (though it nullifies the aeroelastic tailoring you're shooting for).  Note that this requires you to have a symmetric layup schedule, as described in this short course from the US Naval Academy (https://www.usna.edu/Users/mecheng/pjoyce/composites/Short_Course_2003/7_PAX_Short_Course_Laminate-Orientation-Code.pdf).  This isn't the main thrust of your question, however, so I'm not going to delve into it further...it's just a head's up since composites can be more trouble then they are worth, especially if you have access to more traditional machining resources that you can use to make blades out of materials that are easier to shape (plastics, etc.).  The FAA has a nice guidebook too, and, depending on how fluent you are with this stuff, it may be of interest: https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch07.pdf.
If you're not shooting for aeroelastic tailoring or your analysis, for whatever mission you're planning for doesn't show that you get a terrible performance gain, it may be worth it to just try and make a variable pitch mechanism instead.
Alright -- on to inertial properties.  If you're looking to compute the blade's dynamic stability, you'll need inertial properties around multiple axes of rotation to account for the 3 modes of blade motion: blade flapping (i.e., motion of the blade out of plane with the rotation of the propeller), pitching (or twisting), and lagging (motion of the blade in the plane of rotation that occurs in addition to rotation of the blade itself).  Blade stability is related to the coupling of these three modes.  For an application I had (wing of constant cross section, isotropic material), I assumed the following cross section, including a quarter-chord spar and skin.

To solve for the inertial properties of the section (so that I could do a simplified aeroelastic stability analysis), I moved point by point along the airfoil surface.  For example, take the picture below.  It's a zoom in on the upper surface of the previous image.

To find the signed area of a convex polygon, in this case the quadrilateral defined by P1, P2, P3, and P4, the equation is (where x is in the chordwise direction, z is in the vertical direction, and y is the spanwise direction along the blade):
$A=0.5\sum_{i=0}^{n-1}(x_iz_{i+1}-x_{i+1}z_i)= 0.5\left[((x_{P1}\cdot z_{P2})-(x_{P2}\cdot z_{P1})) + ((x_{P2}\cdot z_{P3})-(x_{P3}\cdot z_{P2})) + ...\right]$
...and so on.  Similarly, the centroid can be determined by
$x_c = \frac{1}{6A}\sum_{i=1}^{n-1}(x_i+x_{i+1})(x_iz_{i+1}-x_{i+1}z_i)$
(formulas are most legibly given at https://en.wikipedia.org/wiki/Polygon#Area_and_centroid).  Just use the parallel axis theorem (essentially just weighted average of the centroids and areas) to get all these individual pieces to yield the sectional area and centroid (which, for an isotropic material at least, is the location of your neutral axis).
Moving on the second moment of area (which you'll need for computing stability), it's a similar formula (found at https://en.wikipedia.org/wiki/Second_moment_of_area#Any_polygon):
$I_{xx}=\frac{1}{12}\sum_{i=1}^n(z_i^2+z_iz_{i+1}+z_{i+1}^2)(x_iz_{i+1}-x_{i+1}z_i)$
($I_{zz}$...is similar -- just swap x and z).  Also:
$I_{xz}=\frac{1}{24}\sum_{i=1}^n(x_iz_{i+1}+2x_iz_i+2x_{i+1}z_{i+1}+x_{i+1}z_i)(x_iz_{i+1}-x_{i+1}z_i)$
Apply the parallel axis theorem to get all these individual moments to combine into a sectional property.
Once you have those implemented, the question is just what area do you want to integrate (i.e., is the blade solid, how large is your LE weight, etc.), and what are the elastic properties of those sections.  Then just apply the above.  The out of plane moment of inertia is the sum of the in-plane moments (i.e., $J = (I_{xx}+I_{zz})$).
Finally, as to actually computing dyanamic/static stability, I have a reference text...but it's a set of course notes and I'm not sure the best way to post it as the method is quite involved.  My apologies, but I'm coming up a little short on a good reference for this and may update this question later if I do find something good, however, in the interim, I'd advise you to look at helicopter dynamics texts, which will be a source of material for performance analysis computations too.  One source I could find online is by Bramlette and seems to have the basics well covered, but doesn't venture into rotor stability analysis: http://airspot.ru/book/file/63/bramwell_helicopter_dynamics.pdf

I have read your explanation about the Inertial properties and stability, however i am a bit confused on the axes chosen for the moments and products of Inertia. On the "zoom-in wing skin" figure we have z vs x axis while on moments of inertia working on x and y axis.
Also you mentioned the parallel axis theorem but as i understood, you meant to use it along the span of the blade to find the weighted C.G. What about parallel axis theorem on pitch axis - and C.G axis?
Finally you talking about centroid instead of C.G. Is that because you assumed a constant mass distribution right?

My apologies about the xz vs xy mixup -- I'm so used to using xz ordinates for airfoils, but the formula was stated in xy instead.  I've changed variables in the formulas to be consistent.  As for the parallel axis theorem -- you can use it for more than CG.  I'll write it out in an edit tonight.  And yes, I do just find the centroid of the body for the CG because I assume a constant density, but it's not too different to find the CG of a nonhomogeneous cross section...I'll write that in too.

This is a sketch i have made based  on my understanding on how to use Inertial effects https://i.sstatic.net/qQAiw.jpg
I think there are some similarities with your perspective however i am still confused on which axes i need consider. What about the 3rd axis and therefore moments of inertia related to that axis? and where to define the reference frame coordinate system?
Those are the formulas i 've ended up with:
dm: ρdxdydr;
Offset Pitch Axis - x;
Offset longitudinal Axis - y;
Force: (ρdxdydr)*rω^2 ;
Component along the x-axis: (x/r)Force;
Pitch Moment: y(x/r)*Force

The inertial and mass effects that you should also consider, in addition to what you've already mentioned include blade flapping (i.e., motion of the blade out of plane with the rotation of the propeller), and pitching (or twisting).  Blade stability is related to the coupling of these two modes of blade motion in addition to the one you've already described.  You may want to ask a full, second question about all that stuff.  It's too much for here.

i have uploaded a new question here https://aviation.stackexchange.com/questions/43173/what-inertial-effects-should-be-considered-to-achieve-blade-stability-on-a-varia
Thanks for the assistance anyway


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Is possible to do a private pilot license training and check-ride on a Light Sport Aircraft?
I am planning to do my Private Pilot License. Is it acceptable to do all my training and Check-ride on a LSA?

There should be nothing wrong with that, the problem would be if you were trying to get a Sport Pilots license and did your training on a non-LSA, you would have to take your check ride in an LSA aircraft. If nobody comes up with an answer, I'll write one up later but need to look up the regulations that apply.

Which country/regulations are you asking about?

Related Can hours logged training to be a Sport Pilot apply toward the Private Pilot Certificate?, What does a sport pilot have to do to get a private pilot certificate in the US?, Sport pilot upgrade to private pilot

Consider practical aspects to trying to get a Private Pilot's Cettificate on an LSA.
Will the Certificate be restricted to LSA? Can there be dual instruction on the LSA? (This is a requirement on the instructor for a student and instructor). Is the LSA insured for the purpose? There is no restriction on the type of aircraft on which you can earn a Private Certificate - you can do training on a 747 if that is available - but there are basic requirements, like dual flight instruction. No instructor is going to fly with you unless you demonstrate that you have correct insurance coverage.

The answer is yes. The regulations make no reference to the TYPE of aircraft. Just to the Category and Class. You will need to have at least 3 hours of dual instruction under actual or simulated instrument conditions, flying solely by reference to instruments. As long as this can be done in the particular LSA you are flying, or you achieve it in a different aircraft, it counts.
LSA is neither a Category nor is it a Class of aircraft.
You will have to get a type rating to fly passengers (even not for compensation or hire) if one is required for that aircraft.


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How to decode this METAR published during huricane Harvey?
I have the following METAR from the FAA Aviation Weather Center (AWC) website for KCRP (Corpus Christi Airport):
 KCRP 260551Z AUTO A2935 RMK AO2 SLPNO 6//// 402610239 53014 PWINO

A few questions:

How do we know what the altimeter setting is if the sea level pressure indicator is inoperative?
What does 6//// mean?
What does 402610239 53014 mean?

I suggest changing the title, else this question is of relatively limited interest: the METAR message for KNGP has been already updated with new values.

How to set the altimeter when the "sea level pressure" information is not available?

ATC will be able to provide the information. When aerodrome QNH is not available, the Regional Pressure Setting is used ("safe" setting for the highest location of the region).

6////: Group 6RRRR, 3- and 6-hour precipitation amounts

3- and 6-hour precipitation amounts are missing, sensor not operative or not reachable.

402610239: Group 4snTTTsnTTT, 24-hour max/min temperature in tenths degrees

Maximum temperature in the past 24 hours + 26.1 °C.
Minimum temperature in the past 24 hours + 23.9 °C.

53014: Group 5appp, hourly pressure tendency and and actual change in tenths hPa

Atmospheric pressure now higher than 3 hours ago. Decreasing or steady, then increasing; or increasing then increasing more rapidly.
Variation is 1.4 hPa

PWINO: Sensor status indicators (RVRNO, PWINO, PNO, FZRANO, TSNO, VISNO_LOC, CHINO_LOC)

Precipitation identifier information (rain or snow) not available.

See this decoder and this list of METAR abbreviations.


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How the Log Periodic Dipole Antenna of Localiser help in varying modulation depth?

Here Albert Helfrick speaks about 40% modulation depth for each tone in a localiser radio signal. However latest manuals of ILS manufacturers and google source speaks about 20% modulation depth, not 40%. Albert also says that modulation depth becomes 20% at the centreline of runway.
My question is whether Albert is correct or manufacturers like NORMARC, Thales and SELEX are correct? If Albert is correct then how does 16,20,24
element log periodic dipole array help in achieving this modulation depth variation?
I would appreciate if someone with proper explanation comes up. And this question is not duplicate so please do not confuse it with other modulation varying behaviour of questions asked on this forum.

have you looked at @mins answer to this question?

The array (not required to be made of log-periodic antennas) forms three beams which when combined in space create the various DM for the 90 and 150 Hz tones, and various DDM. This is exactly what is explained in the answer linked by @Gerry. In addition there is a confusion about modulation indexes, explained in this answer.

Mod Depth (more commonly called modulation index in electrical engineering) is the amount a carrier signal is modulated.  Mod depth has nothing to do with antenna configuration and is set by the transmitter (or more precisely the modulator).  The log periodic antenna controls the width of the various beams.  A larger antenna means a smaller beam and smaller beams mean you will have more precision on an ILS approach.  As far as the discrepancy between the 40% and 20% mod depth for ILS systems I will always believe the manufacture.  It seems like the documentation you posted is describing a simple hypothetical setup to help you understand the concept.  I believe most ILS systems use more than two beams. The degree of mod depth shouldn't matter too much as long as your Signal to Noise Ratio is high so I wouldn't get caught with the amount of mod depth in ILS systems.

DLH sorry but its navigation my friend and this concept is different to your electrical equipments stuff !!! I fully understand the wider the antenna the narrower the beam but feed of antenna in ils has strong role in creating mod depth changing effect with respect to azimuth. I am very certain about it. Donot confuse this concept with general modulation index my friend.people dealing with navigation stuff would second my opinion i am sure.

Rumi.  Perhaps I misunderstood your question.  If you are talking about the mod depth variation between the two beams (i.e. space modulation)  Then the characteristics of the antennas does matter.  I thought you were referring to the transmitted signals of the two beams and their mod depth (which is different than space modulation).  Antennas themselves cannot modulate a signal, that was all I was trying to say.  I am sorry if I misunderstood your question.

DLH i appreciate now lets focus and hope someone can comeup with best explanation.


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How fast does cabin air pressure leak after a total engine failure?
When an airliner loses all engines while at cruising altitude, two things happen:

The plane is a glider. It will descend no matter if you want to or not.
The cabin pressure is no longer maintained. Although the valves are closed automatically, they are not air tight - air will slowly leak out until the air pressure is equal to the atmospheric pressure outside.

My question is, which one happens faster? Are the valves able to maintain cabin pressure until the plane has descended to 10,000 feet, or will the oxygen masks deploy before the pilots can complete their descent at best glide speed?

EDIT: For the purpose of the question, let's assume it's s fuel exhaustion and ignore the APU. I'm specifically interested to know if the crew would encounter a situation where they have to choose between oxygen and best glide.

This question mistakenly makes two false assertations: 1) That all airliners have two engines (the 737/747 have more), and 2) That all airliners require the engines running for pressurization (the 787 doesn't).  ;-)  The answer that you are looking for though, is most likely in the maintenance manual.  I have flown other jets which specify a maximum leak rate for the cabin which is checked as part of the maintenance procedures.  (For an idea though, from memory, the value in a Falcon jet is somewhere in the 600-800 fpm range.)

This question cannot be precisely answered since each individual aircraft will have different cabin leak rates.

I don't think the crew must choose between oxygen and best glide. At best glide speed, the sink rate will be great enough to allow oxygen masks to ensure enough breathing before the aircraft reach a flight level where you can breath normally. Even though, this is a quite good question.

@ManuH I actually doubt that is a good assumption. The typical emergency descent due to a loss of pressurization requires a descent near max speed with the airbrakes and/or gear extended in order to get down before running out of oxygen.

@Lnafziger The typical emergency descent is due to a rapid or explosive decompression, though, where the cabin pressure equalizes with the outside pressure immediately. The situation in the question is a gradual cabin leak due to pressurization packs shutting off (due to fuel exhaustion). So it would take much longer for the cabin altitude to climb sufficiently to trigger oxygen mask deployment.

@ElliottTangoFoxtrot Agreed, in this context.  Your statement was more general though and simply said that "At best glide speed, the sink rate will be great enough to allow oxygen masks to ensure enough breathing before the aircraft reach a flight level where you can breath normally." I don't want people to misconstrue that statement in a more general sense.  It's only true here because the masks won't drop until much later in the descent and not at their cruising altitude.

@Lnafziger Gotcha. That wasn't my statement though, it was another commenter's, not that it's a problem.

@ElliottTangoFoxtrot Oops, "The" statement!  :)

The valves will not be able to maintain cabin pressure until the plane descends to 10,000 feet at best glide speed. The oxygen masks will deploy before then.
At least that was the case for Air Transat Flight 236, an A332 that ran out of fuel over the Atlantic and glided to a deadstick landing. The occurrence report on page 96 (see the table) estimates that oxygen masks deployed at 06:37:50, when the cabin altitude reached 13,500 ft. This was about 11.5 minutes after fuel exhaustion, and only 7-8 minutes before landing at 06:45. So they would have landed within the 10 minutes of supplemental oxygen. Even a much longer glide would have allowed them to descend below 10,000 ft before the supplemental oxygen stopped. TSC 236 is AFAIK the longest glide in a transport category aircraft to date, so if they did not "encounter a situation where they have to choose between oxygen and best glide" (to use your phrasing), then probably no one else did either.
Note: The report used the 'worst case' leak rate of 700 ft/min for their calculation. The footnotes explain that the leak rate would decrease as the aircraft descended (because the pressure differential between the cabin and the outside would decrease as the aircraft descended). If anyone is interested, there is more info on pages 28-29 of the report about the cabin pressurization.

Well if a dual engine loss occurred, the APU in the tail also drives a compressor to provide at least limited cabin pressurization until the engines can either be restarted or the aircraft can descend below 14,000 ft ASL.
The emergency RATs in airliners only drive a generator and hydraulic pump, not a compressor to provide cabin air.
Finally even if there was a failure in cabin pressurization because the air supply from engine bleed air or APU, the leak would be reasonably slow so as to allow for a controlled emergency descent.  This combined with the chemical OBOGS to provide supplemental oxygen for the crew and passengers would allow for a safe descent without a high risk of hypoxia.


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What exactly is the meaning of "detent" in aviation?
I come across it in many different situations e.g. "settings changed to flight detent" or "landing altitude changes at first detent". There are other scenarios which I came across in the past, but I don't remember them.
Could someone explain me all the different scenarios and what it really means?

Simply put, it's a tactile click stop on some lever or knob (typically some input with a continuous range), usually used to indicate that there's something special about that position. Depending on the purpose, some may even have lock-out mechanisms for protection.

The word comes from the same root as detain, which means to hold something in place.

@Robusto Does it? MW and OED say detent is from Latin tendere (to stretch), while detain is from Latin de + tenere (away + to hold), both via Old French. So while tendere and tenere are similar, they are not the same verb.

If you drive, you probably use detents every day. Your windshield wiper control stalk probably has detents for the different wiper speeds. If you have an automatic transmission, your transmission lever or stalk probably has detents for each setting. If you have a mouse with a scroll wheel, that wheel might be detented to have a detent for every three (or whatever) lines of scrolling.

Ad “landing altitude changes at first detent”, are you sure you didn't mix up ‘aLtitude’ and ‘aTtitude’? Because I can't think where the first would be true (landing altitude is the airfield altitude, obviously), but since flaps besides increasing lift shift the maximum lift to a lower angle of attack, landing aTtitude does depend on which detent the flap lever is in, in some aircraft quite significantly.

A detent is usually a discontinuity in force at a certain position: the control likes to move into that position, and moving it away takes more than average force.
Image source
In the image above, the flap detents are clearly identifiable as the notches in the guide rail: in order to move the lever away from a notch, it needs to be lifted first and can only then be positioned in a different detent.
The flight control sticks often have a detent that indicates force trim position: on either side of stick travel is a preloaded spring, and the stick can only be moved once the breakout force is exceeded. The rest of the stick travel will then simply increase force proportional with the spring gradient - if released to neutral, the force will gradually decrease until the stick falls into the breakout position.

Thank you very much for your answer.
So in my current case, does this mean the landing altitude changes every time there is a discontinuity in force at a certain position? But then what I don't understand is : Is the landing altitude not set by the pilot (fixed --> landing altitude =runway altitude)? How can landing altitude change at first detent, 2nd detent ?

And note that this isn't specific to aviation -- all kinds of levers, knobs and other mechanisms have detents.

@kg1913 It's much more basic than that. It's a feature of the control itself - the motion of the lever wants to stop at that position and you have to provide extra force to move it out of that position. It will then stop at the next position, and so on. Think of a rotary knob with multiple stops. It "clicks" from one to the next. The impact of what the control actually does to the flight altitude or whatever is completely independent from this concept.

@kg1913 It's a feature of the input mechanism, the effect it has depends on the function of the device that the setting is selected of.

Does the word "detent" also apply to when the discontinuity isn't intentional, but rather the result of (for instance) faulty prouction or wear and tear?

An example most people would be familiar with is when shifting into reverse in a car with a manual transmission; normally there is a detent you need to "push through" to get into (and prevent accidental engagement of) reverse.

Good example, and welcome to Av.SE!

Yes, it impedes from neutral to reverse, but does not impedee between neutral and drive, between which you can switch freely; and should. Simply so you know how the car handles there, and can get it there using muscle memory in an unintended acceleration incident.

A detent can be simply a palpable change in operative force.
Take a wall dimmer: it has free movement in the dimming range. At the lowest dim setting, if you continue, a significantly greater force will snap it past a detent and into "hard off", which causes a plain switch to de-energize the bulb so you can change it.  At the other end is another detent to "hard on", where a plain switch bypasses the dimmer electronics entirely (so they will stop buzzing.)
E.G. if you set throttles to full military, you don't need to release a latch to get it past TO/GA, just the extra force to push past the detent.


text:
Has an earthquake ever complicated or prevented a safe landing/takeoff?
This question on being able to see ground effects of earthquakes from the air got me wondering:
No doubt a severe earthquake at the wrong time could hinder even experienced pilots, but I expect a minor one may be unnoticeable or simply cause a mildly unsteady landing:

"An earthquake--really?  I thought that felt a little weird"

Are there any known instances of an earthquake during approach/landing/takeoff? What were the results?
Naturally if there exists any video that'd be helpful.

I see tag edits here, re-adding and re-removing the 'earthquake' label.  This question deals with more than merely takeoff and landing.  IMO its nature warrants either 'earthquake' or at least 'weather.'  The weather tag existed when I wrote the question, and https://aviation.stackexchange.com/users/675/greg-hewgill created Earthquake in the same spirit.  ...my two cents.

IMO its nature warrants either 'earthquake' or at least 'weather.' (no pun intended)

Yes, there have been aircraft landing at the moment an earthquake hit. Here is an article about one in 2011: Air NZ plane landed as Christchurch earthquake hit

"It was creepy as... as the plane came down, you could see all the windows in the terminal just rolling, and all the shuttles that go out to the plane were in the tarmac just rolling.
"Somebody shouted out 'oh my god, it's an earthquake!'"
"We came down and couldn't get out, and there was a big shake while we were still in the plane. Then we sat there for an hour.

This is of course from the point of view of a passenger, not the pilots.

Dang, that's been eight years already--time, well...flies.  I figured it's had to have happened at one time or another.  I'd be interested in seeing video--I'll update the question with that.  Thanks Greg.


text:
Viability of Magnetically started engines
I am working on a school project of mine which involved testing the viability of a magnetically started jet engine. By magnetically started, I mean that there are magnets which accelerate the main shaft to speed to start the engine. The point of this is to remove the need for an APU, saving space and cost on airliners and military jets.
To provide intake air to the engine to allow it to start up without an APU, there would be a system on the bottom of the engine with small electric fans to push air to the wet section of the engine to start combustion. During the flight the electric fans would be turned off and the intake section would be used like a RAM air intake for the wet section of the engine. The magnets would be powered by the battery in the aircraft, and the small electric fans would be powered by a separate battery in the engine itself.
With all that in mind, would this be viable in a commercial or private environment? Or does the APU do its job too well to replace it?

Even an electrical start system will take a lot of power, probably more suited to an APU than onboard batteries. And I'm having a hard time understanding how these electric fans and ram air intake work with a turbofan engine.

The APU does more than just start the engines...

Magnets start pushing the blades around, while fans in another section of the engine push air via a pipe to the compressor section.   When I said RAM air intake, I mean that when inflight, the electric fans would be turned off, and the air flowing through that section would go into the compressor section. The design (so far) has it so that there is a soft 90 degree angle where the air comes in and is angled into the wet section of the engine. I probably misused the term RAM air intake, but that is the general idea.

I know that the APU has functions other than starting the engines, and that is why this is looking at the viability of this. In the end it could turn out to not be effective, or the mag-start could just take some functions away from the APU, but in my eyes it's an interesting idea and I want to see where it goes.

Is the use of a electrically powered electromagnetic starter generator considered?  What is the compression ratio and flow for the electric fans, and what would the power draw be for that work?

I've voted to put this question on hold because I'm not sure what your specific question actually is.

The Boeing 787 starts its engines using an electric motor (which contains magnets), but it still uses an APU to power that electric motor.

Would these "starting magnets" just be an electric motor? If not, what makes them different from an electric motor?

I thought I understood what you were asking when you were talking about the magnetics, but the "system on the bottom of the engine with small electric fans to push air to the wet section of the engine to start combustion" is not clear.  I wonder if perhaps you have some misconception about how the APU starts an engine in current designs.  Suggest to read this answer: https://aviation.stackexchange.com/questions/33597/how-is-bleed-air-used-to-start-a-jet-engine?rq=1 and then edit your question to clarify that section.  Also I agree with all of points made by @Koyovis

Agreed daniel, i will reword that one for you

Three things come to mind:

Magnets are heavy.
Not all compressor and turbine blades are ferro-magnetic.
The starter would only start the engine, and then be dead weight.

Usually, new designs are implemented when they have clear advantages over previous solutions, but I cannot see what problem this would solve. The APU is a very versatile and lightweight piece of equipment that can power up all of the systems of an airplane. Not really anyone's prime target for replacement, I reckon that captain Sully would agree.


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How is the center of mass controlled in planes with multiple tail engines?
My understanding is that, for flight stability, the center of mass must be ahead of the aerodynamic center.
There have been some rather big jets with 2 or 3 jet engines in the tail. Tu-154 and Boeing 727 have 3 in the tail. The DC-9 has 2, and there seem to be countless small private jets with twin engines in/near the tail, like the Learjet 45.
Another example is the Concorde and Tu-144 which had a whopping 4 engines very near the tail. If I'm not mistaken those were some extra-heavy engines too since they had to be supersonic.
So if we're putting the heavy engines in the tail, what is done to compensate? Do they just use ballast in the nose? How is the center of mass kept under control?
A few more details: Engines at the tail requires stronger (heavier) empennage, which also adds more weight in a direction we do not want our CG moving. Wings still hold the fuel, so moving the large wing/fuel mass backwards just to move the aerodynamic center backwards doesn't seem like enough.
I noticed that those tailed trijets and large tailed twinjets seem rather old. There don't seem to be any new designs of large commercial aircraft with tail jets. This makes me suspicious that the configuration is inefficient. However, small private jets seem to always be tailed twinjets, whether new or old designs.

Move the wings aft and compensate for aft CG with bigger tail surfaces.

@casey it can't be as simple as that because fuel is still stored in the wings. Moving the wings/fuel back also moves the CG backwards too. I'll edit the OP with more details.

I don't think the engines are as far back as you think they are: http://code7700.com/weight_and_balance_principles.html

@DrZ214 yes, the CG moves aft with the wings but this has the benefit that it reduces the moment arm of the engines and increases the moment arm of everything forward of the CG, which helps balance the airplane.  It is a balancing act but that is how they do it.

The wings are placed sufficiently far aft.
Yes, moving the wings aft moves the C/G aft as well, but since the fuselage has some weight, eventually the centre of lift overtakes the centre of gravity and there you place the wings.
A slight problem is that C/G of cargo gets quite a bit ahead of the C/G of the airframe, causing a large difference in overall C/G position between empty and loaded aircraft and a larger horizontal stabilizer is required to maintain control over the whole range. And that, of course, reduces overall efficiency.
When you look at aircraft with tail-mounted engines, you'll see that it has wings further aft compared to one with wing-mounted engines.
Note that Concorde additionally could transfer fuel between forward and aft fuel tank in flight to adjust the C/G in flight to reduce the needed deflection of the elevators. But that was not because of the overall aft C/G—the centre of lift was correspondingly far aft—but because the centre of lift moves quite significantly aft in supersonic flight.


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Why don't we fly helicopters with yokes?
Both yokes and sticks are common in fixed wing aircrafts, with yokes on mainly passenger-carrying aircrafts and sticks mainly on gliders, aerobatic aircrafts and fighter jets.
However I have never seen a helicopter with a yoke-style flight control. Why?

Well first off, a helicopter doesn't have either a yoke or a stick; it has a cyclic.
Second, the original use for a yoke or a stick was to provide a pilot with a mechanical advantage in actuating the airplane's control surfaces against the force of the relative wind.  Helicopters never needed this as the cyclic actuated the swash plate on the rotor mast, changing the pitch of the rotor blades as they passed over.
Third, helicopters demand a little more 'hands on' attention when flying them as opposed to airplanes.  The helicopter pilot is required, particularly in hovering, to make constant adjustments to the cyclic, collective, throttle (if not equipped with a governor) and anti-torque pedals.  Therefore a yoke style cyclic is not useful to a helicopter pilot.
A cyclic does not necessarily need to take the form of a traditional joystick as in the example from an MD900 (Top) and an R22 (bottom).

It's just one stick? What does your left hand operate?

@Mazura the Collective


text:
If all engines fail in a Boeing, how heavy are the flight controls?
Consider a large airliner with no Fly-By-Wire controls, such as a Boeing 747 or 767. All the engines have failed, the Ram Air Turbine is deployed, and the plane is gliding.
How heavy are the flight controls in this situation?
What about Boeing 777 and 787, which are Fly-By-Wire aircrafts?

EDIT: Regarding the question "how heavy", I would like to get a number, or if that's not possible, a description from a pilot whether it is physically exhausting to hold the controls.

IIRC, the captain of the Gimli glider held it in a pretty pronounced sideslip for an extended period of time in order to increase drag and quickly lose altitude. That would have been with no fuel and only the RAT. IIRC it was described as physically demanding, but AFAIR he didn't need physical help from the FO. That should give you an upper bound.

For comparison: In this accident (on a DC-9), where a lavatory fire caused the elevator trim system to fail, the pilot experienced physical exhaustion up to a point where he could not evacuate the plane until being "doused [...] in firefighting foam through [the copilots] window"

To get an idea of the maximum forces, look at the certification limits. FAR 23.143 gives the limits for GA aircraft and FAR 25.143 those for larger aircraft including airliners. If these forces would be exceeded, even when something has failed, the aircraft would not be certified.
The short-term limits in pitch are:

60 lbs for stick-controlled aircraft (only covered in FAR 23),
50 lbs when only one hand is available for control, and
75 lbs when both hands can be used for control.

The short-term limits in roll are:

30 lbs for stick-controlled aircraft (only covered in FAR 23),
25 lbs when only one hand is available for control, and
50 lbs when both hands can be used for control.

The maximum force limits for prolonged application are much lower again.


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What is the history and process of designing new waypoints and airways?
I am interested in what goes into designing new airways and navigation fixes, especially on international routes. For example, after WWII, there were no established international air service. Now, we have waypoints (defined by coordinates), VORs, high and low altitude airways etc. connecting across continents. So at some point in history, somebody decided to add a new airway and a set of fixes to the charts. But exactly how?
Who decide where and what to put on the chart? Is there a panel with representatives from major airlines? Or, if government authorities are involved, what happens to waypoints above international waters?

Have you reviewed TERPS?

FAA Order 8260.3B  I have a 1976 hard copy, there may be newer versions.  This will address most of your questions.  Demand and usage drives airway creations, and TERPS has the criteria for obstructions, etc.


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What is the requirement for fire fighting equipment on board a passenger flight?
What is the legal requirement regarding fire fighting equipment on a passenger flight, e.g. fire extinguishers and fire hoods? I imagine that the number is proportional to the airplane's max capacity.
I'd prefer ICAO since it applies internationally, but if there is none, a FAA reference would be a good as well.

Gas masks? Do you mean oxygen masks? Or fire hoods?

@RonBeyer I mean hoods. Edited.

Aren't they published and can be readily googled?

@Koyovis Published and "easily googled" information are still valid questions, just makes it easier to answer...

There are also mandatory extinguishers for engines /APU and cargo holds.

You have this tagged  both FAA and ICAO but for the FAA thats governed under

§ 121.309 Emergency equipment.
(c)Hand fire extinguishers for crew, passenger, cargo, and galley
  compartments. Hand fire extinguishers of an approved type must be
  provided for use in crew, passenger, cargo, and galley compartments in
  accordance with the following:
(1) The type and quantity of extinguishing agent must be suitable for
  the kinds of fires likely to occur in the compartment where the
  extinguisher is intended to be used and, for passenger compartments,
  must be designed to minimize the hazard of toxic gas concentrations.
(2)Cargo compartments. At least one hand fire extinguisher must be
  conveniently located for use in each class E cargo compartment that is
  accessible to crewmembers during flight.
(3)Galley compartments. At least one hand fire extinguisher must be
  conveniently located for use in each galley located in a compartment
  other than a passenger, cargo, or crew compartment.
(4)Flightcrew compartment. At least one hand fire extinguisher must be
  conveniently located on the flight deck for use by the flightcrew.
(5)Passenger compartments. Hand fire extinguishers for use in
  passenger compartments must be conveniently located and, when two or
  more are required, uniformly distributed throughout each compartment.
  Hand fire extinguishers shall be provided in passenger compartments as
  follows:
(i) For airplanes having passenger se ats accommodating more than 6
  but fewer than 31 passengers, at least one.
(ii) For airplanes having passenger se ats accommodating more than 30
  but fewer than 61 passengers, at least two.
(iii) For airplanes having passenger se ats accommodating more than 60
  passengers, there must be at least the following number of hand fire
  extinguishers:
Minimum Number of Hand Fire Extinguishers Passenger seating
  accommodations:
61 through 200:   3
201 through 300:  4
301 through 400:  5
401 through 500:  6
501 through 600:  7
601 or more:  8
(6) Notwithstanding
  the requirement for uniform distribution of hand fire extinguishers as
  prescribed in paragraph (c)(5) of this section, for those cases where
  a galley is located in a passenger compartment, at least one hand fire
  extinguisher must be conveniently located and easily accessible for
  use in the galley.
(7) At least two of the required hand fire extinguisher installed in
  passenger-carrying airplanes must contain Halon 1211
  (bromochlorofluoromethane) or equivalent as the extinguishing agent.
  At least one hand fire extinguisher in the passenger compartment must
  contain Halon 1211 or equivalent.

You may also find some pertinent info here.

In paragraph no. 1 you mentioned that the type of agent must be suitable to minimize the hazard of toxic gas concentration , at the same time you recommend using hallon gas extinguisher and everyone knows that it is toxic and affects human health why not replace with alternatives of hall9n such as FM200 or etc.

@Saidasad These are not my recommendations they are those of the FAA please see included links.